Various types of linear D.C. motors are known which are capable of developing large forces with reasonable rates of speed and acceleration which are useful, for example, in connection with the constitution of machine carriage drive systems. One of these types of linear motor is constituted by a moving component made of permanent magnets over a coil winding arrangement on soft-iron structure as the fixed component. In this type of motor, the moving magnets assembly beside providing the moving force to the machine carriage, also generates a force perpendicular to the plane of motion. This force is generated by the magnets in regard to the soft iron and it is in reality disturbing and in many cases deforms the structure or stresses it. To alleviate the problem, certain manufacturers put two motors back to back. In this manner, after a fashion, the structure is not stressed significantly. However, the motors become bulky and inertia forces are always present as another additional burden. Such motors may be of the classical commutator bars or brushless type if solid state devices are utilized to reverse electrical current sequentially in the coils. It is desirable, however, to avoid the above-indicated parasitic forces by eliminating the stator soft iron component, thereby suppressing all stresses while keeping only the useful vector force component along the length as described hereinbelow.
There are other types of linear motor/driver systems which areccalled micro steppers. In these motors, advancing forces are generated by external current pulses in windings associated with permanent magnets, to cause mover and stator to advance from one position of magnetic lock into another. These motors may operate up to 12,500 steps/inch even to 25,000 steps/inch. They do not require servo controls and operate in a digital fashion. The position of the mover is never absolutely accurate and can be disturbed by any external force superior to the magnetic lock. The useful vector force they achieve is quite low; 10 lbs. is a good maximum value.